You must absolutely not use the default pool.ntp.org zone names as the default configuration in your application or appliance.

Once you have gone through the process of setting up / obtaining appropriate server address(es) - refer to the pool.ntp.org vendor info page - you can use these in your OE configuration. To do this, use a bbappend for the ntp recipe in your own layer providing ntp.conf and/or ntpdate.default with the appropriate servers set within.